Cbm block reserve estimation using eclipse

3. Objectives:-
Reserve calculation of
CBM block using case
study and comparative
analysis of properties.
Learning the basics of
ECLIPSE for CBM
simulation.
Learning the basics of
CBM block and its
extraction process.

4. What is Coal Bed Methane??
 Standard natural gas- CH4
 Methane forms along with coal
during coalification process.
 Held in the cleats with the coal.
 Held on the surface of the coal
matrix by adsorption.

5. Vitality of CBM Gas Extraction
Energy need
of the nation
is increasing
at
exponential
rate.
Alternative
and non-
conventional
sources of
energy are
becoming
indispensable
.
CBM is a
clean burning
fuel.
Improves
safety of coal
mining and
prevents
firedamp
explosion.
Provides a
means to use
the abundant
coal resource
that is too
deep to mine.
Decrease
methane
vented to the
atmosphere
which might
cause global
warming.
An
unexplored
source of
energy which
has great
economic
potential.

6. CBM and its Dual Porosity

7. Production Profile of a CBM well

8. Relationship Between Rank, Depth
and Sorptive Capacity of CBM

9. Different Simulator used in the
Industry
COMETPC
3-D
• It is used to perform three different types of coal bed methane reservoir simulation
studies.
GEM
• It is by the Computer Modeling Group (CMG) Ltd., and is a compositional reservoir
simulator using a dual porosity system, adsorption, diffusion and additional
features for modeling CBM reservoirs.
• For modeling the diffusion process, GEM uses sorption time, τ, as a direct input.
ECLIPSE
• It is available from Schlumberger.
• For CBM modeling, this simulator uses a dual porosity system applying adsorption,
diffusion and additional features.

10. “ECLIPSE” Simulator Basic
Description
Oil and gas
reservoir simulator
developed by ECL
( Explorations
Consultants
Limited) and owned
by Schlumberger.
ECLIPSE is an
acronym for ECL’s
Implicit Program
for Simulation
Engineering.
It uses finite
volume method to
solve material and
energy balance
equations modeling
a subsurface
reservoir.

11. Data Requirement for CBM
Simulation
Reservoir description data such as geometry, structure, net
thickness, depth, stratification, initial water saturation and pressure.
Fluid PVT data such as gas viscosity and composition and time
dependent well data such as fluid rates and bottom hole pressure.
Absolute cleat permeability which determines rate of gas recovery,
initial gas content for determining gas in place, adsorption isotherm
for determining ultimate gas recovery and cleat porosity which is
site of water storage in coal beds and determines volume of water
produced.

12. Case Study
 A coal seam at Raniganj mine was selected and simulation was
done using ECLIPSE simulator.
 Study was done for a coal seam of approximately “22” acre area.
 Five-spots pattern was built using the ECLIPSE.
 Grid sensitivity study used a single layer grid model of 75×75×1 in
a 5-spots pattern with the dimensions of the coal reservoir
1000×1000×3.64 ft.

13. Model Geometry of 5-point
model

14. Input Data for ECLIPSE Model
Parameter Unit Values
Reservoir drainage area ft2 106
Depth ft. 3050
Reservoir thickness ft. 3.64
Coal- seam porosity % 2.67
Absolute permeability md 1.43
Initial pressure Psia 1392
Rock density g/cc 1.4172
Sorption time Constant days 7
Microbe Diffusion Coefficient ft2 /day 1

15. Input Data for ECLIPSE Model
Parameter Unit Values
Sorption Volume(CH4) scf/ton 578
Sorption Pressure (CH4) Psia 611
Initial water saturation % 100
Initial mole fraction of gas(CH4) % 100
Reservoir Temperature F 113
Well bottom Hole Pressure Psia 40
Well bore Radius ft. 0.5 ft.
Ash Content % 19
Moisture Content % 8
Abandonment Pressure Psia 20

16. Desorption Isotherm for CH4

17. Flow rate v/s Time for Primary
Recovery

18. Total production v/s Time for
Primary Recovery

19. Avg. Pressure Profile

20. Total Field Production Comparison
for Different Sorption Time

21. Field Production Rate for Different
Sorption Time

22. Field Pressure Profile for Different
Sorption Time

23. Field Production Total for Different
Initial Water Saturation

24. Field Production Rate for Different
Initial Water Saturation

25. Field Pressure Profile for Different
Initial Water Saturation

26. CH4 Gas Saturation after 1,3,6,9
and 12 months

27. Results and Conclusions
Total gas content in the coal seam block is 57108847 scf over an area of 106 sq.ft. The
recovery factor for the block is 95.43% for primary recovery process.
Higher saturation of water in coal seam extends the time require to produce the methane
gas and a sufficient length of dewatering period will be required before production of gas.
Sensitivity of production profile indicates that by applying erroneous formulation for
sorption time an incorrect production profile and gas peak will be estimated. So reservoir
simulator which include diffusion for modelling reservoirs instead of combining desorption
isotherm and equation of conventional reservoir will correctly model the production
profile.

28. Future Scope of Project
The project has great scope in calculation of CBM
potential in number of CBM field being developed by
Govt. Of India.
ECLIPSE as a software has been highly successful in
getting correct reserve estimation and sensitivity
analysis and thus could be used extensively in the
industry.
Comparative analysis of gas rate, total production of
CBM et. al. with sorption time, initial water saturation
has proved out to be of great importance in selecting
the block for CBM extraction.

29. References
1. Zuber, M.D. et al.: “The Use of Simulation and History Matching to Determine
Critical Coalbed Methane Reservoir Properties,” paper SPE/DOE 16420
presented at the 1987 SPE/DOE Low Permeability Reservoir Symposium,
Denver, and 18-19 May.
2. Seidle, J.P., and Arri, L.E.: “Use of Conventional Reservoir Models for Coalbed
Methane Simulation,” paper CIM-90/SPE 21599 presented at the 1990
International Technical Meeting, Calgary, 10-13 June.
3. “Comparison of Computation Methods for CBM Performance”, C.A. MORA,
R.A. WATTENBARGER Texas A&M University & S. MCKETTA El Paso
Exploration and Production Company, 8th Canadian International Petroleum
Conference (58th Annual Technical Meeting), Calgary, Alberta, Canada, June 12
– 14, 2007
4. Jalal, J. and Shahab, D.M.: “A Coalbed Methane Reservoir Simulator Designed
for the Independent Producers,” paper SPE 91414 presented at the 2004 SPE
Eastern Regional Meeting, Charleston, West Virginia, 15-17 September.
5. Halliburton handbook : “ Coalbed methane potential (principle and practice) ”.

32. Back Up Slide
Gas in Place Estimation
 CBM models are characterized as a coal/cleat system of equations. Most of the gas is stored in the coal blocks. Gas
storage is dominated by adsorption according to Eq.3.3.1
 Gas concentration, Gc, is a function of the Langmuir Isotherm curve by means of Eq.3.3.2
 Langmuir volume (VL) represents the maximum amount of methane adsorbed on the surface of the coal matrix when
the pressure, P, reaches infinity. This value is asymptotically approached by the isotherm (Fig. 1.3) as the pressure
increases.
 Langmuir pressure (PL) represents the pressure where the amount of adsorbed methane is one half of its maximum
amount, VL.
 For most of the reservoirs, the coal cleats are initially water saturated. However, some reservoirs present free gas in the
cleat system, and in some special cases, there is no water in the cleat system (dry coal). Most of the times, the free gas
in the cleat system volume is very small compared with the gas adsorbed on the surface of the matrix. Gas in Place in
the cleat system is estimated using the volumetric Eq. 3.3.3.
 GIPf = A * h* f * (1-Sw ) / bg…….. ………………………………………............. 3.3.3
 So, the total gas in place is the sum of the adsorbed gas in the matrix system and the
free gas in the cleats as is shown in Eq. 3.3.4
 GIP = GIPs + GIPf

33. Actual and Model CBM Reservoir

34. Comparison of different diffusion model
applied to Coal Bed Methane Reservoir

35. Sorption Time for Modelling
Diffusion Process
 The drainage rate (Fick’s Law) from the coal block can be
expressed using Eq.
 Sorption time, express the diffusion process by means
of Eq.
 By definition, , is the time at which 63.2% of the ultimate
drainage occurs when maintained at constant surrounding
pressure and temperature.
 From laboratory tests (canister test) the diffusivity term
can be estimated and therefrom the sorption time can be
calculated.